Can standing waves be both transverse and longitudinal?
Resonance in musical instruments relies on standing wave.
In a waveguide, we can have both transverse waves and a longitudinal component.
Also, the most commonly observed waves - water waves- are surface waves and there is displacement both longitudinally and vertically. The surface waves 'look' sinusoidal at low amplitudes but become very much more 'peaky' at high amplitude.
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